Adjustable voltage transformer



July 12, 1966 c. G. HOWARD ADJUSTABLE VOLTAGE TRANSFORMER Filed April 8,1964 FRI H INVENTOR.

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United States Patent 3,260,975 ADJUSTABLE VOLTAGE TRANSFORMER Carl G.Howard, 261 Lakeside Place, Highland Park, Ill. Filed Apr. 8, 1964, Ser.No. 358,350

2 Claims. (Cl. 336-433) This invention relates to the art of railwaylighting, particularly at crossings, and more specifically to animproved transformer for such lighting.

Railway signal lights operate at relatively low voltages, generally inthe order of ten to fifteen volts. Where practical, power is supplied bystep-down transformers from power lines, generally with stand-bybatteries to insure proper operation should the power line supply fail.The requirements for power in any given installation can vary quitesubstantially. For example, some intersections or crossings may have aslittle as one or two lights, while others may have as many as sixteenlights. Most transformers have a certain amount of regulation variance,whereby the voltage output changes to a greater or lesser degree withload. The best prior art transformers for this purpose have utilized afixed core and have had a plurality of taps on the secondary or outputwinding. A considerable degree of effort was necessary in order for theinstaller to connect the load to the proper tap or taps to obtain thecorrect voltage.

There is in existence another type of transformer having a core which isin part movable. This allows ready setting of the output voltage toquite a precise level. Unfortunately, prior art transformers of thistype have had very poor output voltage regulation. For example, with aneight lamp circuit with the transformer set at ten volts, if one lampwere to burn out, the voltage might easily go up to as much as fifteenvolts, thus greatly overvoltaging and quickly burning out the remaininglamps.

In view of the foregoing, it is the primary object of this invention toprovide an improved railway signal lighting transformer which is lessexpensive than prior art transformers for this purpose and which givessatisfactory regulation and simplifies adjustment.

It is another object of this invention to provide a nailway signallighting transformer having a micrometer adjustment.

More specifically, it is an object of this invention to provide arailway sign-a1 lighting step-down transformer having a movable coreportion and having a dual output winding providing micrometer adjustmentand satisfactory regulation.

Other and further objects and advantages of the present invention willbe apparent from the following description when taken in connection withthe accompanying figures wherein:

FIG. 1 is a front view of a transformer constructed in accordance withmy present invention;

FIG. 2 is a side view thereof;

FIG. 3 is a horizontal view partly in section taken substantially alongthe line 3-3 in FIG. 1;

FIG. 4 is a fragmentary vertical sectional view taken substantiallyalong the line 44 in FIG. 3; and

FIG. 5 is an electrical wiring diagram of the transformer.

' Referring now in greater particularity to the drawings, and first toFIGS. 1-3, there will be seen a transformer constructed in accordancewith the principles of the present invention. The transformer includes acore 12 of the usual E and I lamination type. The core comprises firstand second upright legs 14 and 16 on which the secondary 18 and primary20 windings are mounted. A third upright leg 22 is spaced to the rightof the secondary coil or winding and all three legs upstand from and areintegral with a base 24. A movable laminated bar or slug 26 is mountedacross the upper ends of the upstanding legs 14, 16 and 22, and themounting structure therefor will be set forth shortly hereinafter.

The core laminations are held together at the bottom by bolts 28extending through apertures in the laminations, and also through theupstanding flange 30 of a bracket 32. The bracket has a horizontal web34, and a rear upstanding flange 36. Both the rear flange 36 and the web34 are provided with apertures for receipt of screws or bolts formounting the transformer. End portions of the bracket web 34 and flange36 extend past the ends of the core 12 to provide access for ascrewdriver or the like for securing the bracket 32 in place. As will beapparent, nuts 40 are threaded on the rear ends of the bolts 28.

A clamping plate 42 is provided at the top of the core and has a nameplate 44 directly in front thereof. Bolts 46, preferably having washersunder the heads thereof, as also is preferably the case with the bolts28, extend through the plates 44 and 42, and also through apertures inthe tops of the vertical legs 14, 16 and 22 of the transformer core. Atthe rear end, these bolts also pass through apertures in an anglebracket 48, and have nuts 50 threaded on the ends thereof, preferablywith washers therebeneath. The angle bracket 48 includes vertical flange52 through which the bolts 46 pass, and also a horizontal flange 54.Bolts 55 pass through apertures in the horizontal flange 54 and alsothrough a horizontal flange 56 of a right angle bracket 58 which alsohas an upstanding vertical wall 60. Nuts 62 are threaded on the bolts 55beneath the flange 56. As may be seen in FIG. 3 the flange 56 is in theform of a pair of ears with a central discontinuity therebetween, exceptfor a rather narrow connecting shelf 64. Similarly, the horizontalflange 54 of the bracket 48 is provided with a central cut out 66. Thecut out and the discontinuity provide clearance for wires, as will beapparent shortly hereinafter.

As readily may be seen in FIGS. 1 and 3, the bracket 58 extends in eachdirection beyond the core 12. The limit at one side is approximatelycoterminous with that of the secondary coil, as is the correspondingportion of the bracket 32. The key hole shaped slots 68 are pro vided inthe vertical flange 60 for mounting the transformer against a verticalwall.

An insulating terminal block 70 is mounted at the upper end of thevertical flange 60 and carries a plurality of binding posts of the screwand nut type at 72 in horizontal alignment and extending from the frontthereof, conveniently with a label plate 74 for indicating theconnections. The insulating block and binding posts are standard, andhence five binding posts are shown. The left and center binding postsare connected to the primary winding 20, while the two right mostbinding posts are connected to thesecondary winding 18.

As will be seen particularly in FIGS. 2, 3, and 4, the magnetic shunt orcore portion 26 rests on top of two or three of the legs 14, 16 and 22and fits closely between the plates 42 and 50. A bolt 76 extends throughthese plates and has a nut '78 on the front thereof for drawing theplates toward one another to clamp the shunt 26 in adjusted position. Aleaf spring member 30 is held down by the bolt 76 against the magneticshunt 26 whereby to hold it down against the tops of the upright legs,and also to provide a frictional resistance to movement.

The front wall 42 and name plate 44 are provided with a horizontallyelongated slot 82. An L-shaped stud 34 extends from the magnetic shunt26 through this slot and is provided with a threaded shank portion $6.This threaded shank portion is received in the nut member 88 having aknurled thumb wheel 96 and an axially extending internally threadedsleeve 92. The sleeve or cylinder 92 is provided with a reduced neckportion 94. The reduced neck is received in a slot or recess 96 in anear or lug 9% formed on the edge of the wall 42 and extending at rightangles therefrom. Thus, with the nut 78 loosened, turning of the thumbwheel 90 will shift the shunt to the left or to the right, according tothe direction of rotation of the thumb wheel. When the proper outputvoltage has been obtained, then the nut 73 is tightened to clamp theplates 42 and 52 against the magnetic shunt, and thereby to hold itfirmly in place.

Reference now should be had to the magnetic and electric circuit of FIG.5. The primary coil previously indicated generally by the numeral 20 isprovided with the leads 100, which go to the left and to the centerbinding posts, as previously indicated. This primary coil is wound onthe center upstanding leg 16. The secondary coil heretofore indicated bythe number 18 is actually a split coil. Somewhat over half of thesecondary coil is wound at 102 on top of or under the primary coil onthe leg 16, and the remainder of the secondary coil is wound at 104 onthe leg 14, the leads to the primary coil being identified at 166, andleading to the two right binding posts, as heretofore noted. The twoportions of the secondary are connected in series additive relationship.

The portion of the secondary winding on top of or under the primarywinding on the leg 16 is suflicient to give the minimum desired outputvoltage. With the magnetic shunt or slug 26 all of the way to the right,it will overlie the legs 16 and 22, but will be spaced slightly to theright of the top of the leg 14. In one actual specimen rated at eightamperes, 13.5 volts, the aforesaid spacing is about one-eighth of aninch, with the total distance across the core amounting to approximatelyfour and three-eighths inches.

As the magnetic shunt is advanced to the left, more voltage is obtainedfrom the Winding 104 of the secondary, and this adds to the voltageobtained from the winding 102. Approximately an additional four volts(could he wound for any voltage) can be obtained by shifting themagnetic shunt all of the way to the left, thus placing substantiallyall of the magnetic flux through the legs 14 and 16, whereassubstantially all of it was through the legs 16 and 22 with the magneticshunt all of the way to the right. Obviously, at intermediate positionspart of the magnetic flux will be through the leg 14, and part throughthe leg 22. The portion of the output voltage obtained from the winding102. is substantially invariable regardless of load, at least withinrated limits. The voltage obtained from the winding portion 104 dropssomewhat with increasing load, but the portion of the output voltageobtained from this winding 104 is never more than about half of thatobtained from the winding portion 102, and hence regulation in thewinding portion 104 is minimized. In actual tests it has been found thatfor load changes of zero to five amperes the total change in voltage isnot more than about one volt, and this is not sutficient to cause rapidburning out of lamps.

In general, it has been found desirable to provide two differenttransformers to cover the range of seven to fourteen volts. Onetransformer is constructed to provide from seven to eleven volts, whilethe second is constructed to provide from ten to fourteen volts. Anyother range of voltage can be provided.

Tests have been performed on such transformers operating With volts onthe primary, and with different settings of the secondary as summarizedhereinafter. Such results are as follows:

N. L. full setting 12.0 1 amp load 12.8 2 amp load 12.8 3 amp load 12.64 amp load 12.2 5 amp load 12.0 N. L. full setting 11.5 1 amp load 12.22 amp load 12.2 3 amp load 12.0 4 amp load 11.8 5 amp load 11.3 N. L.full setting 10.0 1 amp load 10.4 2 amp load 10.2 3 amp load 9.9 4 ampload 9.4 5 amp load 9.2 N. L. full setting 9.5 1 amp load 10.2 2 ampload 10.0 3 amp load 9.8 4 amp load 9.3

Thus, I have been able to produce a transformer with a micrometeradjustment which is built entirely from standard parts, used in otherproducts, thereby maintaining costs at a minimum. The transformer issimple for anyone to use and has satisfactory regulation While providingthe simple micrometer adjustment.

Various changes in structure will no doubt occur to those skilled in theart, and will be understood as forming a part of the invention insofaras they fall within the spirit and scope of the appended claims.

The invention is hereby claimed as follows:

1. A voltage transformer comprising:

(a) a magnetic core having three substantially parallel legs,respectively, a first leg, a second middle leg and a third leg,

(b) means connecting each of said three legs together at a first endportion of said legs,

(0) the second end portion of said legs being separate from each other,there being a first dimension spanning said first and second legs and asecond dimension spanning said first and third legs,

(d) a magnetic shunt movable across said second end portion,

(e) said shunt having a length greater than said first dimension andless than said second dimension, said shunt being adjustably movablefrom a first position spanning said second leg and substantially all ofsaid first leg through a second position spanning all of said second legand parts of both of said first and third legs to a third positionspanning said second leg and substantially all of said third leg andback through said second position to said first position to vary thereluctance of the magnetic path between said first and second legs,

(f) a primary winding on said second middle leg,

(g) a secondary winding on said second middle leg,

(h) said secondary winding on the middle leg providing substantially theminimum rated voltage of said transformer,

(i) a secondary winding 011 the first leg in series addition with thesecondary winding on said second leg, the secondary winding on saidfirst leg providing substantially one-half the voltage of the secondarywinding on the second leg,

(j) screw thread means for moving said magnetic shunt on the second endportion of said three legs, and

5 amp load (k) lock means for locking said magnetic shunt in aReferences Cited by the Examiner predetermined position.

2. A voltage transformer as set forth in claim 1 UNITED STATES PATENTS(l) bracket means is attached to said second end p01' 2192'312 3/1940Holslag 336 135 tion of Said legs, 5 2,248,070 7/ 1941 Fanger 336-433(m) said screw means is mounted on said bracket 3154756 10/1964 Bolarskl336-433 means,

(11) said bracket means provides a channel to guide the ROBERT SCHAEFERy Examine" movement of said magnetic shunt, and JOHN F. BURNS, Examiner.

(0t)h 53613, bracket means has terminal means connected 10 C TORRES,Assistant Examiner.

1. A VOLTAGE TRANSFORMER COMPRISING: (A) A MAGNETIC CORE HAVING THREESUBSTANTIALLY PARALLEL LEGS, RESPECTIVELY, A FIRST LEG, A SECOND MIDDLELEG AND A THIRD LEG, (B) MEANS CONNECTING EACH OF SAID THREE LEGSTOGETHER AT A FIRST END PORTION OF SAID LEGS, (C) THE SECOND END PORTIONOF SAID LEGS BEING SEPARATE FROM EACH OTHER, THERE BEING A FIRSTDIMENSION SPANNING SAID FIRST AND SECOND LEGS AND A SECOND DIMENSIONSPANNING SAID FIRST AND THIRD LEGS, (D) A MAGNETIC SHUNT MOVABLE ACROSSSAID SECOND END PORTION, (E) SAID SHUNT HAVING A LENGTH GREATER THANSAID FIRST DIMENSION AND LESS THAN SAID SECOND DIMENSION, SAID SHUNTBEING ADJUSTABLY MOVABLE FROM A FIRST POSITION SPANNING SAID SECOND LEGAND SUBSTANTIALLY ALL OF SAID FIRST LEG THROUGH A SECOND POSITIONSPANNING ALL OF SAID SECOND LEG AND PARTS OF BOTH OF SAID FIRST POSITIONTO THIRD LEGS TO A THIRD POSITION SPANNING SAID SECOND LEG ANDSUBSTANTIALLY ALL OF SAID THIRD LEG AND BACK THROUGH SAID SECONDPOSITION TO SAID FIRST POSITION TO VARY THE RELUCTANCE OF THE MAGNETICPATH BETWEEN SAID FIRST AND SECOND LEGS, (F) A PRIMARY WINDING ON SAIDSECOND MIDDLE LEG, (G) A SECONDARY WINDING ON SAID SECOND MIDDLE LEG,(H) SAID SECONDRY WINDING ON THE MIDDLE LEG PROVIDING SUBSTANTIALLY THEMINIMUM RATED VOLTAGE OF SAID TRANSFORMER, (I) A SECONDARY WINDING ONTHE FIRST LEG IN SERIES ADDITION WITH THE SECONDARY WINDING ON SAIDSECOND LEG, THE SECONDARY WINDING ON SAID FIRST LEG PROVIDINGSUBSTANTIALLY ONE-HALF THE VOLTAGE OF THE SECONDARY WINDING ON THESECOND LEG, (J) SCREW THREAD MEANS FOR MOVING SAID MAGNETIC SHUNT ON THESECOND END PORTION OF SAID THREE LEGS, AND (K) LOCK MEANS FOR LOCKINGSAID MAGNETIC SHUNT IN A PREDETERMINED POSITION.